The present invention, in some embodiments thereof, relates to LiDAR and aerial mapping of the ground topography, and more particularly but not exclusively to the mapping process using the data obtained from the LiDAR sensor.
LiDAR, an acronym for Light Detection and Ranging, is a sensor that enables rapid generation of dense, accurate, digital models of the topography and vertical structure of a target surface.
The airborne LiDAR laser sensor is mounted on the underside of an aircraft. It transmits pulses of narrow laser beam towards the earth as the aircraft flies. A receiver affixed to the aircraft receives reflections of the pulses as they bounce off the ground surface, and objects on the ground, back to the aircraft. Most LiDAR systems use a scanning mirror to generate a swath of light pulses. Swath width depends on the mirror's angle of oscillation, and the ground-point density depends on factors such as aircraft speed and mirror oscillation rate. Each LiDAR laser reflection provides a single point on the ground. Ranges are determined by computing the amount of time it takes light to leave an airplane, travel to the ground and return to the sensor. The precise position and altitude of a sensing unit, instantaneous scan mirror angle and the collected ranges are used to calculate 3-D positions of terrain and object points from the detected reflections.
The LiDAR data is typically coupled with additional precise positioning information gathered by on board Global Positioning Instruments (GPS) and other Inertial Navigation Systems (INS). Once the total information volume is stored and processed, the result is an extremely accurate “x.y.z.” mapping for every position scanned on the ground.
FIG. 1 shows a basic system in which an aircraft uses a laser beam to scan the ground and detect reflections. GPS data is used to fix the position of the aircraft, with which position the LiDAR data can be correlated to the ground.
LiDAR collects on average 10 points per square meter so a flight that covers 50 Sq. Km acquires approximately 2*1010 data points to be processed, and one of the issues preventing widespread acceptance of LiDAR is the lack of software tools that automatically and efficiently process the LiDAR data. In general today the raw LiDAR data is given to a specialist, who interprets the data in terms of recognizing and indicating structures on the ground. Thus huge numbers of man-hours are spent on LiDAR data, making the final product very expensive.